Building Instructions

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Attach a wire from the left motor to port B on
the NXT and from the right motor to port C on the NXT.

Scribble Pad Programming

Use the
program Scribble Pad for
the Scribble Pad. This program is designed to be as simple as
possible in order to make it easy to understand, so it has a number of
weaknesses. See the Challenges section for ideas on how to improve
it.

How to
Use the Scribble Pad

Use the two dial knobs like an Etch-a-Sketch
to scribble or try to draw something on the screen.

Press the orange button to clear the screen.

Challenges

A classic Etch-a-Sketch
challenge is to draw a circle (or at least something close) which is
amazingly difficult. Give it a try!

Drawing on this
scribble pad is very challenging for several reasons, including:

The dials are hard to
turn because the motors have a lot of resistance.

The dials are too
sensitive (turning just a little draws too much).

When you draw too far
to the right and top, the line disappears off the screen.

When you draw too far
to the left and bottom, the line "bounces back" and starts moving
the other way.

When you double back on
a line, you cannot see where you are.

You cannot "lift your
pen" to put gaps in the drawing.

It is hard to remember
which dial is which, and which way to turn them.

Some of these problems
are due to limitations in the NXT hardware or programming system,
and some are classic Etch-a-Sketch problems, but many of them could
be solved by improving the program or modifying the mechanical
design. For an advanced challenge, can you improve any of
these by modifying the mechanical design or the program?